This invention relates to an assembly and method for delivering and deploying an expandable stent by balloon inflation, particularly within a lumen of a body vessel by means of a catheter assembly. It may be used for deploying other balloon expandable medical devices also, such as filters, grafts and occlusion devices. More specifically, this invention relates to the provision of a novel stent securement body within the stent expanding balloon to enhance the securement of the stent or medical device to the catheter assembly during intraluminal delivery of the stent to a deployment site. In accordance with this invention, the stent securement body comprises a fugitive element of the apparatus.
Stents and stent delivery assemblies are utilized in a number of medical procedures and situations and as such, their structure and function are well known. A stent is a generally cylindrical prosthesis which is introduced via a catheter into a lumen of a body, such as a vessel, in a configuration having a generally reduced diameter and then expanded to the diameter of the vessel. In its expanded configuration, the stent supports and reinforces the vessel walls while maintaining the vessel in an open, unobstructed condition.
Both self-expanding and inflation expandable stents are well known and widely available. Self-expanding stents must be maintained under positive external pressure in order to maintain their reduced diameter configuration during delivery of the stent to its deployment site. Inflation expandable stents (also known as balloon expandable stents) are crimped to their reduced diameter about the delivery catheter, positioned at the deployment site, and then expanded to the vessel diameter by fluid inflation of a balloon positioned between the stent and the delivery catheter. The present invention is particularly concerned with delivery and deployment of balloon expandable stents.
In advancing a balloon expandable stent through a body vessel to the deployment site, the stent must be able to securely maintain its axial position on the delivery catheter.
In positioning a balloon expandable stent on the delivery catheter over the fluid expandable balloon, the stent must be crimped to closely conform to the overall profile of the catheter and the unexpanded balloon.
It is known to make use of a mounting body, positioned about the catheter and within the balloon to provide a seat for the crimped stent. The application of securement pressure to the mounting body component of a catheter assembly provides a good friction fit to the stent and ensures good contact between the stent and the underlying balloon, mounting body and catheter, as already known in the art. The desired diameter of the stent upon the application of securement pressure to the mounting body and crimping recoil is characterized as the xe2x80x9cdelivery diameterxe2x80x9d, because in this condition the stent can safely, reliably and securely be delivered to the pre-selected position within a body vessel. Instead of merely crimping the stent onto the balloon and the underlying catheter and relying on the bulk of the flaccid balloon to hold the stent on, according to the present invention, the mounting body serves as a mounting base.
There are two basic functions to a mounting body. 1) It provides solid underlying material to which to crimp the stent, and 2) it may be shaped or configured to create a mechanical interference fit against axial movement of the stent. However, the presence of the mounting body on the catheter limits the catheter profile or diameter when the balloon is deflated following stent implantation.
According to the present invention, a novel, fugitive stent securement tube, ring, rings or other body, herein collectively referred to as a xe2x80x9cmounting bodyxe2x80x9d, is/are positioned within the expandable balloon to aid in securing the stent to the balloon and the catheter during delivery.
Accordingly, the present invention comprises an improved assembly for delivery and deployment of an inflation expandable stent within a vessel. The assembly comprises a catheter, a fugitive mounting body carried on the catheter, an expandable balloon mounted on the catheter and encompassing the mounting body and a stent mounted on the balloon. The catheter has proximal and distal ends. The stent is inflation expandable from a delivery diameter to a deployment diameter. The delivery diameter is reduced from the manufactured diameter for conforming the stent to the catheter. The stent, in its delivery diameter, is coaxially mounted on the catheter near the catheter distal end. The expandable balloon is coaxially mounted on the catheter axially within the stent. The balloon is designed and adapted for expansion of the stent from the delivery diameter to the deployment diameter upon application of fluid deployment pressure to the balloon. The mounting body is coaxially mounted on the catheter, axially within the expandable balloon. The mounting body is preferably substantially equal in length to the stent and the stent is positioned on the assembly preferably coextensive with the mounting body. However, it may be of different size and configurations.
The mounting body is fugitive in that it is made of a softenable, more preferably a dissolvable or biodegradable material, which will remain solid up to deployment of the stent, but will soften or dissolve thereafter. The fugitive nature of the mounting body is important in allowing for the minimization of the diameter size or lower profile of the balloon/catheter for ease of withdrawal after the stent has been deployed.
In another aspect, this invention comprises a method for delivering and deploying a stent using an assembly as just described. A catheter is provided having proximal and distal ends. An expandable balloon is coaxially mounted on the catheter. A fugitive mounting body is coaxially mounted on the catheter, axially within the expandable balloon. The balloon is initially in an unexpanded condition. A stent is provided which is expandable from a delivery diameter to a deployment diameter. The stent, in a diameter greater than the delivery diameter, is initially mounted on the balloon. The stent is then collapsed to the delivery diameter to conform to an overall profile of the catheter, the mounting body and the balloon. The mounting body provides a mounting base for the balloon/stent in the delivery diameter. The assembly is delivered to a deployment site. The balloon is inflated to expand the stent to its deployment diameter. The mounting body remains solid through delivery of the stent to the lesion site. Upon inflation of the balloon, the bulk material of the mounting body softens or more preferably dissolves in the saline/contrast solution or other fluid used to inflate the balloon thus allowing for a minimal low profile when the balloon is deflated.